#include <stdio.h>
#define PI 3.1415926//符号常量
int main(){
    //定义一个变量名字时的规则
    int readInt=0;
    int read_int=0;
    //int readint 不推荐
    int var1, val2, val3;
    char ch1;//先声明 后使用
    ch1 ='A';
    printf("%c\n",ch1);
    //PI 是一个常量 数值不可更改
    float area = PI*1.5*1.5;
    0==1;//0=1 不合法
    signed int oVar = 0127;//signed可以省略
    unsigned int ox1 ;//unsigned不可以省略
    int oxVar = 0x23FF;
    printf("%d bytes for integer.\n",sizeof(int));
    signed int test_int = -2;
    printf("the singned test_int is:%d\n", test_int);// %d 有符号的十进制输出 
    printf("the unsigned test_int is:%u\n", test_int);
    int signed_int = -2u;
    printf("signed int is:%d",signed_int);
    
    return 0;
}